Placing a 4XX HTTP standing code to get a canonicalized URL has a similar impact as using the noindex tag: Google might be not able to begin to see the canonical tag and, consequently, can’t transfer “link equity” for the canonical version. Perhaps somebody have designed it with GTM ? https://bookmarkzap.com/story18717633/how-was-ist-canonical-tag-can-save-you-time-stress-and-money